Understood.
My best guess:
They have an issue with the app they have installed, so they go to the Play page. But as your app have a similar name and icon, they mistakenly pick that one instead. Which means they also send their email to you, and not the makers of the actual app they have installed.
You should try to convert them to use your app instead. Something like:
"Hi there!
Thanks for your email, but I'm sorry - that's not our app. Don't worry, it's easy to pick the wrong one in the app store, you're not alone in doing so.
However, I'm glad to let you know that the issue you're talking about isn't in our app, and we have thousands of very happy users. They tend to like that it is really easy to do x, y and z.
Why not install it and see if it works better for you? Here's the link to the app again: xyz.
Have a great day!"